A fluorinated polymer such as a polytetrafluoroethylene (hereinafter referred to as PTFE), a melt-processable fluororesin or a fluoroelastomer is produced by emulsion polymerization of a fluorinated monomer using an anionic fluorinated emulsifier (hereinafter referred to as AFE).
Since the AFE is not easily decomposed in the natural world, in recent years, it is required to reduce an anionic fluorinated emulsifier contained in industrial effluents and in products such as a fluorinated polymer aqueous dispersion, etc.
Usually, a fluorinated polymer aqueous dispersion (hereinafter referred to as AD) is produced by adding a nonionic surfactant (hereinafter referred to as NSAA) to a fluorinated polymer aqueous emulsion obtained by emulsion polymerization to stabilize the emulsion, followed by concentration. On that occasion, the AD containing the AFE is brought into contact with a basic ion exchange resin (hereinafter referred to as a basic IER) so that the AFE is adsorbed on the basic IER, thereby to reduce the content of the AFE in the AD. Since the AFE is expensive, attempts have been made to recover and recycle the AFE adsorbed on the basic IER.
For example, Patent Document 1 discloses a method of treating a basic IER having an AFE adsorbed thereon, with a mixture of a dilute mineral acid and an organic solvent, to recover the AFE as an acid. It is disclosed that the organic solvent is preferably a solvent which is miscible with water to present a solubility of at least 40% or which can be unlimitedly mixed with water, and an alcohol such as methanol, a cyclic ether such as dioxane, methylene chloride, etc. may be used.
In Examples in Patent Document 1, the AFE was recovered with a high yield of at least 80% from a weakly basic IER using as the organic solvent an alcohol such as methanol or a cyclic ether such dioxane.
In Examples in Patent Document 2, the AFE was recovered with a high yield of at least 80% from a basic IER using an aqueous inorganic acid solution, an organic solvent having a nitrile group and a fluorinated medium. However, it was found that since the basic IER having the AFE adsorbed thereon obtained in the step of reducing the AFE in the AD, has the NSAA physically adsorbed thereon, when the acid of the AFE is separated and purified, the recovery rate of the AFE is lowered by influences of the NSAA and its decomposed products.